To provide a discrimination device and a discrimination method capable of discriminating a road surface state.

An on-vehicle device calculates a distance conversion coefficient at the points of time of passing respective points P10, P11, ... in a road surface state determining area (a determination area) P1. When a vehicle runs in the area P1, the on-vehicle device acquires a plurality of distance conversion coefficients (the number of points P10, P11, ...) as time series data in real time, and discriminates (determines) a road surface state, that is, a dry road surface (a non-rainfall state) or a wet road surface (a state during or after rain fall) according to a statistical distribution (a frequency distribution) of the time series data of the acquired distance conversion coefficients.